The requirement for automatic testing and chemical control of specific parameters in water and water bodies in the domestic, commercial and industrial sectors is increasingly demanded by both operators and governing bodies. The health risks associated with incorrectly managed pool or cooling tower water has created an awareness of the need for reliable automatic monitoring and treatment systems. Recent outbreaks of infection from the pathogens Giardia and Cryptosporidium contacted from commercial swimming pools and the numerous Legionella infections contracted from air conditioning water towers highlights the needs for stringent chemical testing. Government standards now often specify testing of commercial swimming pools or cooling towers be performed multiple times per day and the results must be entered into a log book for audit. Given the increasing awareness of bow important regular monitoring of water bodies such as swimming pools and cooling tows is, there is a need for an apparatus for mixing and/or testing small fluid samples which is capable of, at least to some extent, alleviating the often laborious task of regular testing and balance alteration.
Sanitisers generally used in the field of water treatment, such as the treatment of water cooling towers used in multi-story buildings, domestic and public pools and spas, include chlorine, chlorine dioxide, hydrogen peroxide, ozone and bromine and combinations of these. The use of chlorine dioxide in the sanitisation of water is a relatively new phenomenon and is gaining popularity worldwide. It is especially effective against the pathogens, Giardia and Cryptosporidium and has been used extensively during outbreaks of these pathogens in swimming pools and drinking water during the year 2000 it Australia Chlorine dioxide must be produced in situ as it is unstable. For this reason, it is not sold in pre-packaged containers for consumer or commercial use. Chlorine dioxide is a dark yellow coloured gas. It may exist as gas dissolved in solution, but has a short shelf life. Principally there are two ways of producing chlorine dioxide, by the oxidation of chlorite or the reduction of chlorates. A simple method of production is to add sodium chloride to an acid in the correct proportions. However this process is particularly dangerous and it is not recommended that novices attempt to correctly mix the solutions. If the process is performed incorrectly, the chlorine dioxide gas may not remain dissolved in the solution and may evaporate out of solution to form a toxic gas cloud causing severe respiratory problems. Even relatively small airborne concentrations of chlorine dioxide may cause respiratory difficulties in those who su from asthma. Accordingly, there is a need for an apparatus capable of overcoming these safety issues to make available to novices the ability to use this excellent sanitiser chlorine dioxide, to treat the water body in question.
Automatic collection of samples of water for colormetric analysis has been limited to the use of flow through cells. These cells are normally used for colormetric analysis of the sample with any reagent introduced by means of a peristaltic pump. After introducing a reagent into the flow cell vial, a magnetic rod mixes the solution and the colorimetric analysis is performed. However, there is a concern with these flow through cells in applications such as swimming pools and spas where algae or mineral build up may line the inside of the cells whereby reducing their effectiveness by a affecting the optical transparency which they originally possessed. Consequently, inaccurate readings may result if regular cleaning of the cell is not performed. Accordingly, there is a need for an apparatus adapted for the colorimetric analysis of water samples using reagents which involves a less onerous cleaning regime.
Automatic control systems designed to test specific water parameters and react to correct the parameter that requires correction have been described, but are not necessarily widely known. These systems typically utilise probes and are usually positioned in the recirculating system associated with a water body to be treated the system interprets particular parameter values and, based on the results, a mechanical or electronic device may be activated to correct the value in question. The system may pump in liquid chlorine to increase the chlorine level or pump in hydrochloric acid to reduce the pH, for example.
In the case of swimming pools, spas and cooling towers, two water tests which may be automatically performed by this type of equipment are: (1) a measurement of the sanitiser level; and (2) a test of the pH level of the water. The correct control of these two parameters is most critical in preventing the growth of pathogens. Other tests may be required, but the prior art system using probes is not adapted to test parameters such as calcium hardness, total alkalinity and cyanuric acid or stabiliser levels. These tests are conventionally performed manually.
An oxidation redox potential (ORP) probe is typically used by these prior art devices to determine the redox potential or effectiveness of the sanitiser in question. The redox potential reading (expressed in millivolts) is dependent on the pH of the sample. A pH shift of only 0.5 mV upwards may result in excessive corrosive sanitiser levels developing. A downwards pH shift (more acidic) may result in inadequate sanitiser levels. Moreover, a correct chlorine determination and control becomes difficult with such ORP systems if the pH is not accurately monitored and stabilised. Another disadvantage is that the probes require regular cleaning and, furthermore, the instruments require regular calibration.
Whereas commercial operators may adhere to strict procedures which will help these ORP systems produce satisfactory results, novice user have been found to be less assiduous in following correct procedure. Moreover, many of these probes are very sensitive to the movement and velocity of water around them and minor alterations in localised water currents may effect the probe's ability to provide correct readings. Another disadvantage is that although this method may be useful in some instances, the redox potential output is not able to be interpreted in terms of parts per million in relation to sanitiser levels. As the person skilled in the art will appreciate, most world standards require that the sanitiser level be expressed in terms of parts per million. Accordingly, given the stands required in most jurisdictions, users of such ORP devices would still be required to perform standard manual sanitiser tests. In terms of commercial accessibility, ORP systems are expensive and generally out of the price range of the typical domestic pool owner.
As with ORP systems, an automatic method for pH testing using a pH probe has been described. The pH probe is placed in the water circuit and the pH is constantly monitored. An electric signal from the probe to a measuring device determines the pH and in situ in a water treatment plant, if the pH is outside a set range, normally a pump is activated to deliver a chemical to a system to correct the pH. These pH probes also require regular cleaning and become inaccurate if maintenance is ignored.
A disadvantage of both ORP and pH probes is that they are susceptible to producing incorrect values when hydrogen gas bubbles are in the test sample. The hydrogen gas interferes with the chemical reaction associated with the probe. Microscopic hydrogen bubbles are particularly evident in salt chlorination installations fitted to, for example, a pool. This very popular electrolytic method of chlorinating mild saline water systems produces hydrogen gas as a by product of the electrolytic reaction. It would be an advantage to have a colorimetric apparatus which is not affected by the presence of hydrogen gas in the test sample.
The above description of the prior art is not intended to be, nor should it be interpreted as, an indication of the common general knowledge pertaining to the invention, but rather to assist the person skilled in the art in understanding the developmental process which lead to the invention.